fodrv7

fodrv7

Well Known Member
Recently there has been the odd post regarding Engine Failure Glide Angle of RV Aircraft. Generating a lot of opinion, but little hard data.

Today, I flew a number of Climbs at various airspeeds and by selecting my GRT (Grand Rapids) EFIS to "Record" and was able to just concentrate on accurate flying. After landing, I ?Replayed? the flights whilst parked on the apron and casually wrote down the data! ????.. Oooh technology!

The GRT displays GMT, so recording the times through each altitude was a breeze.

After reaching 10,000' for the fifth time, I fondled the throttle closed, progressively, in order to sooth my glorious Aero Sport Power IO-360M1B, selected "Record" and when the throttle was closed, pulled the mixture lean, stopped the prop, trimmed for 80KT and let the GRT record the data.

Pushed the nose down and a windmill start had the fan turning at 120KT.

Back on the ground the data showed a decent rate of 882fpm and 902fpm timed between 8000' & 7000' and 7000' & 6000'

This equates to a glide ratio of 9:1.

So there it is.

Let the discussion begin.
Pete.
 
Great work Peter! I hope that you saved the data file, becasue you can run it through Carl Morgan's GRT Decoder and get even more precision and extract more info.

I might be slow, but are your two numbers (882 and 902 fpm) the values with prop stopped and prop windmilling respectively? And I forget your configuration - which prop?

I love it when folks post REAL data!

Paul
 
How did you get 9:1?

How did you get 9:1? Did you maintain 120 kts indicated for the data points you listed? If so, I get 15.5:1. Here's my math

882 fpm = 14.7 fps
120 kts indicated @ 8000 ft = 228.5 fps true

gamma = asin(14.7 / 228.5) = 3.688 degrees (flight path angle)

1/tan(gamma)=15.5

Thus I get 15.5:1


Also, can you estimate your gross weight when you conducted the glide test? Thanks.

Alex
 
Glide

Alex said:
How did you get 9:1? Did you maintain 120 kts indicated for the data points you listed? If so, I get 15.5:1. Here's my math

882 fpm = 14.7 fps
120 kts indicated @ 8000 ft = 228.5 fps true

gamma = asin(14.7 / 228.5) = 3.688 degrees (flight path angle)

1/tan(gamma)=15.5

Thus I get 15.5:1


Also, can you estimate your gross weight when you conducted the glide test? Thanks.

Alex
Click to expand...

I believe the glide was at 80Kt (120 was to get the prop spinning).
Also, weight does not affect glide ratio. It does affect the speed for best L/D, so it would be good to see this done for a few other speeds.

Dennis Glaeser
7A - fuselage
 
Capt Zero.

Sorry, fellas. I was a bit vague with the details.

Previously I had found that the best glide L/D was around 70KT, but there is no way I would want to do a forced landing and cross the fence at 70KT as I am sure you would run out of airspeed in the flare.

So the figures were obtained at 80KT.

I would like to go and do it again with:
Prop full fine.
Prop full coarse
Prop Stopped
for comparasion.

Today was dead calm with DALR 0f 2?C. I will need to wait for another similar day.

I have already sent the file to Carl for decode and his amusement.

When I replayed the flight I was writing down the Altitudes and times from the PFD. I then selected ENG and there were all the Engine figures?. Except RPM which was zero.

Pete.
 
Oops

Missed the 80 kts number in your initial post. Sorry! :rolleyes:

I see how you got 9:1 now, if you take Vtrue=Vindicated, or if the 80 kts figure was GPS speed. That comes out to 6.2 degrees flight path angle, which seems pretty good to me.

BTW if you use standard atmosphere and calculate Vtrue=90.3 kts @ 8000 ft, then you get 10.3:1.
 
Hey Mike,

So could you elaborate a bit on your power-off to touchdown testing? I've done the 10K down to 2K glide tests with my 9a, but I'm wondering your setup to take it down to the ground. (runway size, preparation, etc?)
 
Circle to land approaches. 5k' runway at sea level. (I was at KPGD at the time)
Aim for mid field, and you might make the numbers. After a couple of tries, you get the hang of the tremebdous sink rate in a turn to rouchdown. Deployed flaps at about 50' agl.

Making a spot landing is quite a chore prop stopped, but you can do it with practice.
Now go pull that red knob out and try it. ( :eek: Oh my god he told people to shut their engine down). Yes I did. Its my advice and you can take it or leave it. All normal blah blah blah caveats apply. Practice high, work your way down to zero agl. If you think your nervous now to stop the engine, wait till it happens when you not fully prepared. Dont wait for that day to come. Being a glider is no big deal.
Idle (making some power) is not the same and not even close when you are on the last 500'.
Just my observation with my limited flight experience compared to some. And I have had an engine quite completely at the most unopportune time in an RV so I know it CAN happen to me .
Best
 
fodrv7 said:
This equates to a glide ratio of 9:1.

So there it is.

Let the discussion begin.
Pete.
Click to expand...

This is exactly what the cafefoundation reported for the RV8. So it sounds like you're about where you should be. They also reported 900-1000 fpm poweroff descent rate so, again, you seem to be in the ballpark.
 
Stupid me.

Stupid Me.

80KT IAS at 8000' and 11?C = 93KT TAS.

As we always quote Glide as a ratio and not an angle, no need for Tan of the Angle here.

93KT x 6080 (Ft per NM) / 60 (Mins per Hour) gives forward speed in fpm.
=9424 horiz fpm.
Divided by 900 vert fpm = 10.5 : 1

But of course the Glide Angle at 8000? doesn?t matter a whole lot. Unless you are trying to dead stick it at that Leadville joint. Appropriate name for the manoeuvre though.

Mike, it is interesting that your IO-540 won't windmill start. Too little Aluminium trying to push to big an engine. It probably means that the difference between glide at full fine and full coarse is very significant.
Impressed with your approach to the dead stick and maintaining your currency.
Pete.
 
Inverted at 400' for a dead stick.

Having started this thread I feel obliged to offer a word of caution.

Dead sticking an RV, could bring you undone very quickly.

What may be a little demanding for some one like Mike Stewart, could be beyond the ability of a less experienced pilot. If you read Mike?s de-brief on his engine failure from 400? he says, ?I made a 6 G pull, 130 deg. bank left?.
130? is inverted. Anyone done that recently?
But it is a good way to get back to the field, as long as you know what you are doing. But just because Mike is comfortable with dead sticking it, doesn?t mean it is a piece of cake.

Forgive me while I digress a bit here.
Flying Instructors fly pretty well. Which is interesting, as they aren?t meant to be doing much flying. The student should be doing it. But they ARE sitting there watching, intently if they have a sense of survival, for now and then something different happens. In Medieval Times, I remember calling for more power in a Beagle Pup, as we ran into windshear around 20? and how much power I ended up ramming on, when I realised the student wasn?t doing anything. Years later as an FO, I remember seeing an instant 15KT windshear at 20? in a DC-9. The resulting impact destroyed the captains ego, but not the mighty-9.

So what did these experiences teach. Well, they demonstrate that you can get ?enough? instant power from a piston engine to save the embarrassment, but not from a turbine with a 5 sec spool up time. They teach that experienced pilots still get caught.

But the real lesson is how quickly you can run out of energy near the ground; which in the Dead Stick case means AIRSPEED!!!!!!!!!

Back to the issue.
But lots of gliders do dead sticks every day, I hear you say. Yes, but check the aspect ratio of the wings.

The RV has a VERY Low aspect ratio wing.

It doesn?t matter on the cruise, as at low angles of attack Induced Drag (Wing Tip Vortices) is negligible
However, at low airspeeds and high Angles of attack;
Induced drag increases significantly and;
the LOWER the aspect ratio the HIGHER the induced drag.

If you are a little slow or a little low or have a high sink rate, or heavens forgive, any combination of the above, and need a firm pull on the stick for the flare, the drag will rise dramatically, as you crank the wing up to a High Angle of Attack, the speed will wash off at an equally alarming rate and????????? you will no longer be flying.

So, if you have a need to try this dead stick thing, find a long runway like Mike?s 5k. 10k would be better. Then, I would work up to it, using progressively less power on approach until you can nail a glide approach REPEATEDLY with the engine at idle before going for the dead stick.

AND WATCH THE AIRSPEED ON FINAL.
Pete.
 
Inflight re-start of a stopped prop

Another note of caution.
We always DEMONSTRATED a windmill start to students.
One student (not mine) went out to do aeros and rang up to say he had landed in a cabbage patch.
He had stopped the prop in a stall turn and was not successful in attempting a windmill start.
When quizzed about using the starter he said; ?No one told him you could use the starter airborne.?
You can.

If you do a windmill start, make sure the throttle is closed. The RPM will come up very quickly once the engine gets over compression.
Pete.
 
fodrv7 said:
80KT IAS at 8000' and 11?C = 93KT TAS.

As we always quote Glide as a ratio and not an angle, no need for Tan of the Angle here.

93KT x 6080 (Ft per NM) / 60 (Mins per Hour) gives forward speed in fpm.
=9424 horiz fpm.
Divided by 900 vert fpm = 10.5 : 1
Click to expand...
There is also a small temperature correction on the altitude loss. The temperature was a bit warmer than standard, so 1000 ft of barometric altitude change represents a bit more than 1000 ft of geometric altitude loss. The correction factor is equal to the actual temperature divided by the standard temperature, with both values in absolute temperatures (i.e. degrees Kelvin, or Rankin). In this case, assuming no ram rise on the OAT value, the correction factor is about 4.4%. I.e. 900 ft/mn barometric rate of descent = 940 ft/mn geometric rate of descent.

I assume that the EFIS provides an accurate rate of descent. We couldn't make that assumption if you had been using a conventional round-dial VSI. They can be quite inaccurate. Any one who has a conventional mechanical VSI should use a stop watch to time against the altimeter if they want to gather data for climb or glide testing.

There was a flight test in one of the general aviation magazines about 15 years ago, reporting on the performance improvement of putting a 300 hp O-520 in a Beech Debonair. The author was very impressed with the 5,000 ft/mn rate of climb. I wrote a very polite letter to the editor suggesting that they spend a bit more time reviewing the articles, as the reported rate of climb had to be wrong. The known laws of physics simply wouldn't allow 300 hp to drag that much weight up at 5,000 ft/mn. They never printed the letter, but I got a rebuttal letter from the author, who was very upset that I was calling him a liar. I carefully explained my calculations, and said that there had to be something wrong with the flight test data. A while later, a package arrived in the mail. It contained a video tape, with the camera pointing at the VSI, as the aircraft climbed after take-off. Sure enough, the VSI sat at around 5,000 ft/mn. But, you could also see the altimeter in the view, and I timed the altitude change with a stop watch. The altimeter showed a rate of climb of about 1,600 ft/mn. I sent that info to the author, and several weeks later I got a very apologetic letter from the author.
 
Best Glide Ratio

fodrv7 said:
Previously I had found that the best glide L/D was around 70KT
Pete.
Click to expand...

I believe that the speed that you refer to as "best glide L/D" in your note actually refers to a Minimum Sink Speed, or Best Endurance Glide Speed.

The optimum value for Glide Ratio should occur at the Best Range Glide Speed in still air. The CAFE report for the RV-8A found that the Minimum Sink/ Best Endurance Speed at 1723 # gross weight occurred at 81.6 mph CAS, and the Best Range "Vy, Best Glide, Clean" was at 106.8 mph CAS, producing a 9.5 glide ratio (I assume the latter point was probably obtained using the CAFE "zero thrust" crankshaft sensor.)

There are two other data points listed that are quite interesting with respect to the effect of the propellor:

Best Glide, clean, idle, Coarse Pitch 9.2 Glide Ratio @ 96.2 mph CAS

Best Glide, clean, idle, Fine Pitch 7.3 Glide Ratio @ 96.2 mph CAS

Regards, Hawkeye
 
Min Sink and best LD

Hawkeye,
Of course you are right.
My figures are Min Sink.

Kevin,
You always blow me away with all the little things I overlook or don't even know about. Very educational. Thank you. Oh! By the way. It is always ISA + X?C in Australia.

I would have to do a lot more and lot more accurate testing to establish the Best LD and Min Sink Speed.
I started the post because there was a previous post before I had a flying aircraft, asking what was the expected LD for engine failure.
No one came up with an 'actual' figure. Hence, my test flight.

In this regard -engine failure- the Airspeed that you 'ought' to use will be higher than the best LD and certainly higher than the Min Sink.

When glider pilots join the circuit the first thing they do is to increase speed 10-15KT above Best LD Speed and trim for that speed. (More dynamic energy in the aircraft.)
On final they fly high (More potential energy in the aircraft.) and then use speed brakes, which can be retracted to flatten the glide if you are getting low.

The exact Best LD Speed for the RV is therefore a little academic.
In the event you need the best LD, you ought to have some margin above it.

And although there was a desire in the previous post for an answer to "How many miles can I fly from, say, 5000'." this too is academic.

Anyone who selects 'Nearest Airports' on his GPS and starts doing mental arithmetic is not going to make it.

EVERYONE should be able to look out of the cockpit and point to a field that they KNOW they could reach by eyeballing it. And you can only do that if from time to time you close the throttle and test your self.

Preferable onto a 15K' runway. And I would say at at a minimum of 80KT.

Pete.
 
when my engine quit me, when something went thru the injection system, the prop stopped. On my second flight.

I was 2,500 agl and a mile from the airport so I never ever looked inside, just kept coasting for those numbers on the runway.
 
So how is it done.

Congratulations on pulling it off.

Would appreciate a bit of a discription.
Speed and how the speed held from 20'
Pete.
 
Tell us more

Yes, Mark, please do share more information about this event. I'm sure we can all learn something. Congrats on getting it back to earth safely!
 
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